Summary

Hemoglobin, the familiar oxygen-carrying molecule in red blood cells, may have been leading a double life. A group at the Duke University Medical Center reported in the 21 March issue of Nature that, alongside the familiar respiratory cycle, hemoglobin carries out a second cycle in which it sops up a form of nitric oxide in the lungs and releases it in blood vessels—a shuttle service that helps stabilize blood pressure. Besides giving hemoglobin a surprising new role, the finding could be a boon for efforts to turn cell-free hemoglobin solutions, which now tend to produce dangerous rises in blood pressure, into workable blood substitutes.